Choosing the Right Dry Gas Seals for Your Application

Dry gas seals are an important component of modern compressors and turbomachinery. Unlike conventional oil seals, these seals are mechanical and have a thin film of clean gas between the rotating and stationary faces, so that they do not come into direct contact. This design lowers wear and tear, increases service life and limits leakage of hazardous gases.

The selection of the right dry gas seal is not a minor choice, as it has a direct effect on uptime, operating costs and overall safety of the plant. A wrong choice may result in a disaster, unforeseen shutdown, or even safety hazards. Conversely, choosing an appropriate seal leads to smooth operations and reliability in the long term.

Why is choosing the right dry gas seal important?

Before looking at the selection factors, it's worth knowing why the choice of a dry gas seal is so critical.

Minimizes downtime

Unplanned shutdowns can be among the most expensive events in industrial operations. Seal-related problems contribute to up to 48% of the compressor failures. In companies that deal with oil, gas or petrochemical products, it can cost tens of thousands of dollars per hour of downtime.

The purpose of dry gas seals is to provide reliability and long Mean Time Between Failures (MTBF). By using the right seal according to the operating conditions, you can greatly decrease the chances of premature failure and costly downtimes.

Reduces maintenance costs

The conventional wet seals require lubricating oil systems, filtration and regular maintenance. By removing these requirements, dry gas seals make compressor design easier and less costly to operate. The cumulative effect of this is a substantial saving on oil consumption and disposal, as well as costs on system maintenance over time.

Plants that use dry gas seals reduce their sealing system maintenance cost by up to 50% over older oil-lubricated designs. 

Ensures safety 

In plants where hazardous, flammable or toxic gases are used, seal performance relates directly to the safety of the working environment. Dry gas seal offers a much superior containment standard compared to the wet seals. Most of them are designed to keep the leakage below 10 ppm at a maximum pressure of 400 bar.

This is essential in accordance with high standards of environmental and safety laws. The prevention of gas leaks can keep the workers safe, reduce the fire-related risks, and minimize the consequences of the environmental impact. Choosing an appropriate seal to suit your process will help your facility operate with maximum safety.

6 Factors to consider when choosing a Dry Gas Seal for your application

The next step is to review the primary factors that will influence the choice of the dry gas seal that will best suit your application.

Operating pressure

The pressure level is one of the most critical elements in seal selection. Different types of dry gas seals: single, tandem, and double, are designed to handle different ranges of pressure and risk.

• Single seals may be applied where the gas is clean and non-hazardous, and the pressure is moderate.

• Tandem seals are used in high-pressure applications where a backup system is necessary in the event of failure.

• Double seals provide maximum safety, using buffer gas between two seals to handle toxic or explosive gases.

If you have a process such as high-pressure natural gas, petrochemical fluids or hydrogen, then the seal will need to be specifically designed to hold up under these conditions.

Operating temperature

Temperature can affect both seal face materials and secondary components like elastomers. High-temperature processes require seals made up of durable materials like silicon carbide or tungsten carbide with a special coating.

For example, refinery compressors can work at temperatures of more than 200°C. Under these conditions, the improper choice of material can lead to thermal deformation or fast wear. Making sure that the material is compatible with your operating environment is critical to performance.

Fluid properties

Not all gases behave in the same manner, i.e., natural gas, hydrogen and corrosive chemical vapors. For example, hydrogen molecules are tiny and this exposes them to a high probability of escaping through poor seals. That's why you need special designs with closer tolerances when working with hydrogen.

Contaminants in process gas can also shorten seal life. Research shows 43% of dry gas seal failures are due to contamination of the seal gas supply, while 34% occur from process gas contamination during standstill. This highlights the importance of ensuring that there is a clean, dry and filtered gas supply: this is equally as important as the seal choice itself.

Safety considerations

One of the main considerations in the selection of seals is safety, especially in those industries that work with toxic or explosive gases. Tandem or double seals are often required to meet API 692 or ISO requirements, to deliver redundancy and to minimize escaping gas risk.

The design of the seal is not the only factor to be addressed when safety is a priority; auxiliary systems, including gas conditioning units, should be taken into account as well. The right type of seal, together with a dependable support system, gives the best protection against leakage.

Mean Time Between Failures (MTBF)

The reliability of a seal can be determined by its MTBF. Turbomachinery studies indicate that appropriately chosen and maintained dry gas seals have a predicted MTBF of 4 to 6 years. 

Conversely, a wrong match of seals can break within less than two years, leading to an unexpected shutdown. This explains why it is worthwhile to invest time to match the seal specifications with the operating conditions. An extended MTBF not only saves money but also balances production schedules.

Budget

Budget will always be an issue that will influence the selection of equipment. A cheap general-purpose seal may seem like a good alternative initially, but it may prove to be more costly in the long run: because of frequent fixes, shorter service life, and an unresponsive period.

Special seals designed to withstand harsh conditions or hazards come ar a higher premium but can save money in the long run. Choosing a dry seal based solely on price can lead to higher total costs over the equipment lifecycle.

Final thoughts

The appropriate selection of a dry gas seal is more than just a technical specification; it is a commitment to reliability, cost saving, and a safe work environment. By taking into account the operating pressure, temperature, fluid characteristics, safety issues, MTBF and budget, you can decide which seal suits your application best.

When looking to buy reliable and robust dry seals for your application, check out our dry gas seal series. We offer a wide range of reliable dry gas seals tailored to diverse industries and performance needs.